The Ljungström Air Preheater 1920 An International Historic Mechanical Engineering Landmark June 21, 1995 Stockholm, Sweden SMR Svenska Mekanisters Riksförening American Society of Mechanical Engineers Stockholm 1920 The Ljungström Air Preheater The inventor Fredrik Ljungström from the Ljungström Medal Historical Significance of Landmark Throughout the history of boilers there have been many advancements in order to obtain a better per- formance and lower fuel consumption. However, few inventions have been as successful in saving fuel as Economic Impact of the Landmark the Ljungström Air Preheater invented by Fredrik The use of a Ljungström Air Preheater in a modern Ljungström, then Technical Director at Aktiebolaget boiler plant saves a considerable quantity of fuel - so Ljungström Ångturbin (ALÅ). The first installation much that the cost of the preheater is generally re- in a commercial boiler saved as much as 25% of the covered after only a few months. It has been esti- fuel consumption. In a modern utility boiler the mated that the total world-wide fuel savings result- Ljungström Air Preheater provides up to 20% of the ing from all Ljungström Air Preheaters which have total heat transfer in the boiler process, but the been in service is equivalent to 4,500,000,000 tonnes Ljungström Air Preheater only represents 2% of the (4,960,000,000 tons) of oil. An estimate shows that investment. the Ljungström Air Preheaters in operation annually saves about $30 Billion US. The distribution of ther- The Ljungström Air Preheater is a remarkable in- mal power capacity in which Ljungström Air vention in many ways. About 20,000 had been sup- Preheaters are installed over the world is shown in plied to all corners of the globe by 1994. It has been the table below. The estimated distribution of annual estimated that the total operating hours amassed by saving in $US can also be found in the table below: all Ljungström Air Preheaters amount to about 1,500,000,000. Continent Installed Saving capacity % $BUS/year The earliest installations of the Ljungström Air GW Africa 65 5 1.6 Preheater have been taken out of service because the North America 471 30 6.6 fact that the boiler plants have been torn down, con- South America 3 5 2 0.7 sequently the ASME International Historic Mechani- Asia 370 24 7.7 cal Engineering Landmark is placed at Tekniska CIS 216 14 3.8 Museet in Stockholm with a permanent exhibition Europe 365 23 7.6 comprising a working model earlier used for experi- Oceania 38 2 0.5 ments 1961 - 77 at Svenska Rotor Maskiner AB. TOTAL 1560 100 28.5 Landmark Contribution to Develop- ment of New World Wide Industry The use of the Ljungström Air Preheater started in the 1920:s throughout the whole world. In the be- ginning the marketing of the Ljungström Air Preheater was made in close connection with ALÅ, but most of the deliveries have actually been made Figure 1. The landmarked model of the Ljungström Air through a network of licensees throughout the world. Preheater at Tekniska Museet, Stockholm. 2 Licensees 1923 Svenska Maskinverken AB, Sweden James Howden & Co., G:t Britain* Maskin & Brobyggnad, Finland 1924 Smulders, Belgium* Nebrich, Czechoslovakia Gefia, Austria 1925 Oekonomia/Ganz, Hungary* Feuerungstechnik, Germany Lammers & Maase, Germany 1926 Air Preheater Company, USA* 1927 Gadelius, Japan* Babcock & Wilcox, France* 1930 Luftvorwärmer, Germany Sulzer, Switzerland 1932 Hueck & Büren, Germany Julius Pinsch, Germany 1933 Wiesner, Czechoslovakia 1934 Kraftanlagen Heidelberg, Germany* 1935 Dano, Denmark Skoda, Czechoslovakia Witkowitz, Czechoslovakia Cegielski, Poland 1936 Simmering, Austria* 1937 Erste Brünner, Czechoslovakia* Figure 2. Principles of the Ljungström Air Preheate Ceskomoravska, Czechoslovakia 1942 Venezia, Italy* Holima, the Netherlands* Breda, Italy* 1943 Ansaldo, Italy* Ljungström Air Preheaters are used primarily in 1947 Tosi, Italy* boiler plants for preheating the combustion air. In 1949 Gefia, Genua, Italy recent years, their use has expanded to include en- 1952 Tampella, Finland ergy recovery in combination with removal of ox- 1957 Ganz, Hungary* 1958 Burmeister & Wain, Denmark ides of sulphur and nitrogen from flue gases some- 1959 Rafako, Poland* times using catalyst coated heating element plates. 1967 Stein, France* * Still licensee of SRM Special Features and Characteristics The Ljungström Air Preheater is a regenerative heat exchanger, and comprises a slowly rotating rotor filled with heat transfer plates. The hot and cold gas ducts are arranged so that half of the rotor is in the flue gas duct and the other half is in the primary air duct which supplies combustion air to the furnace. The hot flue gases heat the part of the rotor in their path, and as the rotor rotates, the hot section moves into the path of the combustion air and preheats it. The rotor is divided into a number of sections which pass through seals in order to prevent the flue gases Figure 3. Span of sizes for Ljungström Air Preheaters, and the combustion air from mixing. from 0.8 to over 20 m diameter (2.5 to 66 ft) 3 A rotor in a Ljungström Air Preheater may be over paper as heating elements. The first prototype 20m (66ft) in diameter and up to a couple of metres preheater was then later installed at the factory boiler (8ft) thick. The total weight of such a rotor may be at Gåshaga. up to 1,000 tonnes (1,100 tons). The flue gases nor- mally enter the rotor at a temperature of about 350 °C (660 °F), and are cooled to about 120 °C (250 °F) in flowing through it. These temperatures may vary somewhat, depending on the type of fuel. Gas flow rates through the largest preheaters are of the order of 2 million Nm³/h (70 million standard ft³/hr) on each side, and the temperature effectiveness, the quo- tient between the temperature drop of one side and the maximal available temperature difference, is typi- cally 85%. An advantage of the Ljungström method over other methods is that the temperature of the flue gases can be reduced below the sulphuric acid dew point without causing problems. In a recuperative heat exchanger, in which the heat flows through a Figure 4. The first prototype of the Ljungström Air separating wall, the efficiency falls off rapidly if the Preheater at Gåshaga temperature is reduced below the dew point, as de- posits form on the heat transfer surfaces and act as a thermal barrier. On the other hand, deposits on the surfaces of a Ljungström Air Preheater have no meas- urable effect on heat transfer performance. The first commercial installation of the Ljungström Air Preheater was made in 1922 for AB Förenade Choklad Fabrikerna (a chocolate manufacturer) on A Ljungström Air Preheater is also relatively insen- the island of Kungsholmen in Stockholm. sitive to corrosion. Any parts that do corrode away can be easily replaced at a modest cost, and leakage of air to the flue gas side is not affected by corrosion of the heat transfer plates. Historical Development The brothers Birger and Fredrik Ljungström founded Aktiebolaget Ljungström Ångturbin (ALÅ) on Feb- ruary 29, 1908 for development of the double rotat- ing steam turbine. The manufacture of this invention was made in Finspång at the subsidiary Svenska Turbinaktiebolaget Ljungström (STAL). ASEA took over STAL in 1916 from ALÅ, while the develop- ment and the manufacture of turbine-powered loco- motives was started at Gåshaga on the island of Lidingö nearby Stockholm. During a dinner at the Operakällaren Restaurant in Stockholm, Fredrik Ljungström, who suffered from asthma, was both- ered by the dense clouds of cigar smoke and started to wonder how it might be possible to improve the ventilation without losing heat. Using his own idea from 1895 with corrugated heat exchanger elements applied in a high pressure steam boiler resulted in the idea of the regenerative heat exchanger, and the Figure 5. Report from performance measurements at Ljungström Air Preheater was born. The first tests AB Förenade Choklad Fabrikerna. (United Chocolate were performed in ALÅ’s facilities at Gåshaga with Factories) 4 Technical Data for Typical Data for today's sizes of the Coal Fired Grate Boiler Ljungström Air Preheater Data for the hand fired boiler before and after the The sizes of boilers have since then increased and installation of Ljungström Air Preheater is as fol- below typical data for a modern installation is: lows: Boiler Size (electrical output) 300 MW 500 MW Before After Fuel Coal Oil Calorific value of coal 6940 7020 Ljungström Air Preheater Size 2 x 28.5 2 x 30 Date of measurement 1922-03-20 1922-03-21 Diameter (m) 9.9 1 1.4 Fuel consumption (kg/h) 350 288 Area (m²) 73 97 Water evaporated (kg/h) 2100 2180 Height(m) 2.0 1.8 Rotation speed (rpm) 2 Average Steam Temperature (C°) 330.7 330 2 Gas flow (Nm³/h) 450 000 610 000 Average Steam Pressure (kg/m²) 9.8 9.9 Air flow (Nm³/h) 430 000 575 000 Feed water temperature (C°) 4.,5 4.5 Gas temperature in (C°) 375 375 Gas temperature in (C°) 322 Gas temperature out (C°) 120 140 Gas temperature out (C°) 330 166 Air temperature in (C°) 3 5 50 Air temperature in (C°) 40 Air temperature out (C°) 325 324 Air temperature out (C°) 238 Effectiveness, air side (%) 85.4 84.2 Effectiveness, air side (%) 70.2 Effectiveness, gas side (%) 74.9 72. 5 Effectiveness, gas side (%) 55.3 Thermal efficiency of boiler 59.3 74.3 After the first successful installations of the Ljungström Gas Heater Ljungström Air Preheater, it was introduced on the market world-wide as a means of saving fuel in boil- The growing pressure reduce emissions from boil- ers.